Random access method and signaling method for the same

ABSTRACT

A method for performing a random access procedure by a Node-B with a specific user equipment (UE) within a cell in which a plurality of UEs are located together. System information is transmitted for at least one of a basic sequence index and a length of a zero correlation zone (ZCZ) to the specific UE. A preamble sequence is received from the specific UE over a random access channel. The preamble sequence is generated from Constant Amplitude Zero Auto-Correlation (CAZAC) sequences distinguishable by at least one of the basic sequence index and a length of a Cyclic Shift (CS) applied to the preamble sequence. The length of the CS applied to the preamble sequence is given by one among a plurality of application lengths determined based on the length of the ZCZ. A number of the plurality of lengths are differently given based on a type of the specific UE.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a Continuation of U.S. application Ser. No.14/480,356 filed on Sep. 8, 2014 (now U.S. Pat. No. 9,088,993, issued onJul. 21, 2015), which is a Continuation of U.S. patent application Ser.No. 13/843,182 (now U.S. Pat. No. 8,861,473, issued on Oct. 14, 2014)filed on Mar. 15, 2013, which is a Continuation of U.S. patentapplication Ser. No. 12/987,884 (now U.S. Pat. No. 8,422,451, issued onApr. 16, 2013) filed on Jan. 10, 2011, which is a Continuation of U.S.patent application Ser. No. 12/443,121 (now U.S. Pat. No. 7,894,396,issued on Feb. 22, 2011) filed on Mar. 26, 2009, which is the NationalPhase of PCT/KR2007/004637 filed on Sep. 21, 2007, which claims priorityunder 35 U.S.C. §119(e) to U.S. Provisional Application No. 60/827,018filed on Sep. 26, 2006, and which under 35 U.S.C. §119(a) claims thepriority benefit of Patent Application No. 10-2006-0097254 filed in theRepublic of Korea on Oct. 2, 2006, all of which are hereby expresslyincorporated by reference into the present application.

BACKGROUND OF THE INVENTION

1. Technical Field

The present invention relates to a wireless communication technology,and more particularly to a method for generating an iterative sequence,and a method for transmitting a signal using the creating method.

2. Background Art

Presently, a variety of uplink channels for use in a communicationsystem have been discussed, for example, a random access channel (RACH)for allowing a user equipment (UE) to access a Node-B, and an uplinkshared channel (e.g., HS-DPCCH) for transmitting a channel qualityindicator (CQI) and ACK/NACK information.

The RACH channel allows the user equipment (UE) to establish downlinksynchronization with the Node-B, and can be found by information of theNode-B. Location or other information of a corresponding channel can berecognized on the basis of the Node-B information. The RACH channel isthe only one channel to which the user equipment (UE) unsynchronizedwith the Node-B gains access.

If the user equipment (UE) transmits a signal to a corresponding Node-Bover the RACH channel, the Node-B informs the user equipment (UE) of notonly correction information of an uplink signal timing point at whichthe user equipment (UE) is synchronized with the Node-B, but also avariety of information capable of enabling a corresponding UE to accessthe Node-B. If the user equipment (UE) is connected to the Node-B overthe RACH channel, it may communicate with the Node-B over other uplinkchannels.

FIGS. 1 and 2 are conceptual diagrams illustrating a variety ofprocesses encountered when the user equipment (UE) establishes an uplinkcommunication with the Node-B.

If the user equipment (UE) accesses the RACH channel, it can acquireboth uplink and downlink synchronizations associated with the Node-B, sothat it can access a corresponding Node-B.

FIG. 1 shows a specific state in which the user equipment (UE) ispowered on and is firstly connected to the Node-B. FIG. 2 shows anotherstate, in which the user equipment (UE) is unsynchronized with theNode-B after establishing synchronization with the Node-B, or it mustrequest uplink resources from the Node-B after establishingsynchronization with the Node-B (i.e., it requests resources for uplinktransmission data).

As shown in step (1) of FIGS. 1 and 2, the user equipment (UE) transmitsan access preamble to the Node-B. If required, the user equipment (UE)may further transmit a message to the Node-B. Therefore, the Node-Brecognizes why the corresponding user equipment (UE) accesses the RACHchannel, so that it can conduct a necessary process corresponding to therecognized reason.

In the case of the initial access shown in FIG. 1, the Node-B assignstiming information and uplink data resources to a corresponding userequipment (UE), so that the user equipment (UE) can transmit uplink dataas shown in step (4) of FIG. 1.

In the meantime, the exemplary case of FIG. 2 indicates that the userequipment (UE) accesses the RACH channel due to a scheduling request.

Referring to FIG. 2, the Node-B assigns timing information and resourcesfor the scheduling request (SR) at step (2). The Node-B receives thescheduling request (SR) from the user equipment (UE) at step (3), andassigns uplink data resources to the user equipment (UE) at step (4), sothat the user equipment (UE) can transmit uplink data to the Node-B atstep (5).

If the user equipment (UE) accesses the RACH channel using the case ofFIG. 2 instead of the initial access of FIG. 1, it is determined whetherthe signal transmitted to the RACH channel has been synchronized withthe Node-B, so that the user equipment (UE) may transmit differentsignals according to the determined result.

FIG. 3 is a configuration diagram illustrating a RACH signal structureused for a synchronization access and a non-synchronization access.

In the case of the synchronization access, the user equipment (UE)accesses the RACH channel on the condition that it has been synchronizedwith the Node-B and have continuously maintained the synchronizationwith the Node-B.

In this case, it should be noted that the synchronization between theuser equipment (UE) and the Node-B can be maintained by either adownlink signal or control information (e.g., a CQ pilot) delivered toan uplink. The Node-B can easily recognize the signal contained in theRACH channel. And, because the synchronization between the userequipment (UE) and the Node-B has been maintained, the user equipment(UE) may use a longer sequence shown in an upper part of FIG. 3, or maytransmit additional data to the Node-B.

In the case of the non-synchronization access, if a non-synchronizationstate between the user equipment (UE) and the Node-B is provided whilethe user equipment (UE) accesses the Node-B, a guard time shown in alower part of FIG. 3 must be established while the user equipment (UE)accesses the RACH channel. The guard time is established and determinedin consideration of a maximum round-trip delay which can be owned by theuser equipment (UE) which desires to receive any service from theNode-B.

Besides the above-mentioned synchronization and non-synchronizationaccesses, the RACH channel must satisfy different requirements accordingto locations of the UE within a cell (hereinafter referred to as UE'sin-cell locations).

FIG. 4 is a conceptual diagram illustrating different requirementsaccording to UE's location within a cell.

Referring to FIG. 4, an edge area of a cell supported by a Node-B isdetermined to be “R3”, a UE existing in the R3 area is determined to be“UE3”, a specific area existing in an intermediate part of a cell isdetermined to be “R2”, a UE existing in the R2 area is determined to be“UE2”, a specific area close to the Node-B is determined to be “R1”, anda UE existing in the R1 area is determined to be “UE1”. Detaileddescriptions of the above-mentioned cases are shown in FIG. 4.

Referring to FIG. 4, a path loss of the UE1 is denoted by L_(p) ¹, apath loss of the UE2 is denoted by L_(p) ², and a path loss of the UE3is denoted by L_(p) ³. A round-trip delay (RTD) of the UE1 is denoted by2t_(d) ¹, a round-trip delay (RTD) of the UE2 is denoted by 2t_(d) ²,and a round-trip delay (RTD) of the UE3 is denoted by 2t_(d) ³.

In this case, 2t_(d) ¹ indicates that the RTD is double the delay valueof t_(d) ¹ consumed for one-way transmission, 2t_(d) ² indicates thatthe RTD is double the delay value of t_(d) ² consumed for one-waytransmission, and 2t_(d) ³ indicates that the RTD is double the delayvalue of t_(d) ³ consumed for one-way transmission.

Generally, the longer the distance, the higher the path loss, resultingin L_(p) ¹<L_(p) ²<L_(p) ³ and 2t_(d) ¹<2t_(d) ²<2t_(d) ³.

Therefore, the lengths G_(d) ¹, G_(d) ², and G_(d) ³ of individual guardintervals required according to in-cell locations of UE1, UE2, and UE3are denoted by G_(d) ¹<G_(d) ²<G_(d) ³. The expansion coefficients S_(p)¹, S_(p) ², and S_(p) ³ of sequences to be applied to the channel aredenoted by S_(p) ¹<S_(p) ²<S_(p) ³.

In other words, compared with the UE1, the UE3 must access the RACHchannel with a sequence having both a longer RACH and a higher expansioncoefficient in order to acquire the same performance as that of the UE1which accesses the RACH channel with both a shorter RACH and a lowerexpansion coefficient.

The UE1 uses the RACH channel assigned by the Node-B. However, if a cellradius is very long, the RACH size is designed to be appropriate for apredetermined condition for supporting an edge UE (e.g., UE3) of thecell.

Therefore, if any UE such as the UE1 is located close to the Node-B, theUE need not use the long RACH. The case of FIG. 4 indicates that a timelength of the UE1's RACH is longer than that of the UE3's RACH and abandwidth of the UE1's RACH is wider than that of the UE3's RACH.

The above-mentioned method, which satisfies different conditionsrequired for the RACH channel according to the UE's location within acell to effectively perform the RACH communication, and implementseffective communication by defining the RACH length/width and sequencein different ways to implement effective communication, has beendisclosed in Korean Patent Application No. 2006-74764 filed by the sameapplicant as the present invention, entitled “METHOD FORTRANSMITTING/RECEIVING SIGNAL IN COMMUNICATION SYSTEM”, and KoreanPatent Application No. 2006-92835 filed by the same applicant, entitled“RANDOM ACCESS CHANNEL FOR SEGMENTED ACCESS, SEQUENCE, AND METHOD ANDAPPARATUS FOR TRANSMITTING SIGNAL USING THE SAME”.

And, another method, which requires RACH access reasons different inUE's locations within a cell, and differently allocates the RACHsequence used for each area within the cell according to therelationship between the RACH sequence and another sequence used for aneighboring cell, has been disclosed in Korean Patent Application No.2006-87290 filed by the same applicant as the present invention,entitled “SEQUENCE SET FOR RANDOM ACCESS CHANNEL, AND METHOD FORDEFINING THE SEQUENCE SET, AND METHOD AND APPARATUS FOR TRANSMITTINGSIGNAL USING THE SEQUENCE SET”, and Korean Patent Application No.2006-92836 filed by the same applicant, entitled “SEQUENCE ALLOCATIONMETHOD, AND METHOD AND APPARATUS FOR TRANSMITTING SIGNAL USING THEALLOCATED SEQUENCE”.

The above-mentioned methods can effectively use resources according tothe UE's location within a cell, and can access the RACH channel. Ifdifferent sequences are allocated to individual areas, theabove-mentioned methods can reduce the possibility of generating a RACHcollision caused by the same sequence, and can increase the number ofrandom access opportunities of each UE.

In order to allow the user equipment (UE) to access the RACH, the userequipment (UE) must select/transmit predetermined signals. The bestsequence from among the predetermined signals is a Constant AmplitudeZero Auto-Correlation (CAZAC) sequence. The CAZAC sequence has superiorpower-derating characteristics, and can easily make an orthogonalsequence set using a circular shift (CS).

In this case, a correlation value between the CAZAC sequences to whichdifferent circular shifts (CSs) are applied is set to “0”. Theorthogonal sequence set is indicative of the set of sequences, each ofwhich has the corresponding value of “0”.

In association with the above-mentioned description, the degree of CSavailable in the same CAZAC sequence is defined by a zero-correlationzone (ZCZ). The ZCZ width is determined within a predetermined range inwhich a reception end has no difficulty in distinguishing the CAZACsequences.

Besides the above-mentioned advantages, the CAZAC sequences have a verylow cross-correlation value between random sequences, so that they canbe distinguished from each other.

The 3GPP LTE has defined that the above-mentioned CAZAC sequences can beapplied to the RACH, and has assumed that the CAZAC sequences can berepeatedly extended according to the cell sizes.

In other words, a given basic sequence is firstly designed to besuitable for a given RACH length. If a longer spreading gain isrequired, the basic sequence may be repeatedly used.

However, if the sequence is repeatedly used, the 3GPP LTE does notdefine how to extend each basic sequence. Therefore, if the sequence isextended in the form of an iterative sequence, the 3GPP LTE hasdifficulty in determining whether or not to repeat the CP along with thepreamble, and also has difficulty in determining how to set the numberof iterations. In addition, the 3GPP LTE has difficulty in determiningthe length of CP or ZCZ contained in the sequence, and has no solutionof how to decide a signal transmission method.

SUMMARY OF THE INVENTION

Accordingly, the present invention is directed to a random access methodand a signaling method for the same that substantially obviate one ormore problems due to limitations and disadvantages of the related art.

An object of the present invention is to provide a method for generatingan iterative sequence to define consideration items including therepetition of a CP, the number of iterative CPs, and the length of CPand/or ZCZ.

Another object of the present invention is to provide a method forrecognizing a category of information required for signal transmissionusing the extended sequence, acquiring the category information, andgenerating an effective sequence using the acquired information.

Additional advantages, objects, and features of the invention will beset forth in part in the description which follows and in part willbecome apparent to those having ordinary skill in the art uponexamination of the following or may be learned from practice of theinvention. The objectives and other advantages of the invention may berealized and attained by the structure particularly pointed out in thewritten description and claims hereof as well as the appended drawings.

To achieve these objects and other advantages and in accordance with thepurpose of the invention, as embodied and broadly described herein, amethod for allowing a user equipment (UE) to establish a random accesswith a Node-B comprising: selecting a predetermined sequence from asequence set including a plurality of sequences distinguishable by atleast one of a sequence index and a circular shift (CS) degree; andtransmitting the selected sequence to the Node-B over a predeterminedchannel for the random access, wherein the sequence set's unit length towhich the circular shift (CS) is applied is differently determined inproportion to a cell size.

Preferably, before performing the sequence selecting step, the methodfurther comprises receiving at least one of information of the unitlength to which the circular shift (CS) is applied and information ofthe sequence index from the Node-B.

Preferably, the information received from the Node-B is received over abroadcast channel (BCH).

Preferably, the sequence selecting step includes allowing the userequipment (UE) to select the sequence according to the informationreceived from the Node-B.

Preferably, the length of a cyclic prefix (CP) in the sequence set isdifferently determined in proportion to the cell size.

Preferably, the method further comprises, before performing the sequenceselecting step, receiving at least one of information of the unit lengthto which the circular shift (CS) is applied, information of the sequenceindex, and information of the cyclic prefix from the Node-B.

Preferably, the sequence set additionally and differently determines theunit length to which the circular shift (CS) is applied in proportion toa distance between the user equipment (UE) and the Node-B.

Preferably, the unit length to which the circular shift (CS) is appliedis determined in consideration of a round trip delay (RTD) proportionalto the cell size.

Preferably, the sequences distinguishable by at least one of thesequence index and the circular shift (CS) degree are Constant AmplitudeZero Auto-Correlation (CAZAC) sequences.

In another aspect of the present invention, there is provided a methodfor allowing a user equipment (UE) to establish a random access with aNode-B comprising: selecting a predetermined sequence from a sequenceset including a plurality of sequences distinguishable by at least oneof a sequence index and a circular shift (CS) degree; and transmittingthe selected sequence to the Node-B over a predetermined channel for therandom access, wherein the sequence set's unit length to which thecircular shift (CS) applied is constant irrespective of a cell size, andan available sequence is differently determined according to the cellsize.

In yet another aspect of the present invention, there is provided amethod for allowing a Node-B to perform a signaling process for a randomaccess of at least one user equipment (UE), the method comprising:performing the random access of the at least one user equipment (UE) bytransmitting predetermined sequences distinguishable by at least one ofa sequence index and a circular shift (CS) degree; and transmitting atleast one of information of the unit length to which the circular shift(CS) applied and information of the sequence index to the at least oneuser equipment (UE).

In yet another aspect of the present invention, there is provided Amethod for generating a sequence in a user equipment (UE) comprising:selecting a basic sequence; and repeating the basic sequence inproportion to a larger cell size, and extending the basic sequence,wherein a cyclic prefix (CP) of the basic sequence in the extending stepis repeated at least one time so that the basic sequence is extended.

In yet another aspect of the present invention, there is provided amethod for generating a sequence in a user equipment (UE) comprising:selecting a basic sequence; and repeating the basic sequence inproportion to a longer distance to a Node-B, and extending the basicsequence, wherein a cyclic prefix (CP) of the basic sequence in theextending step is repeated at least one time so that the basic sequenceis extended.

Preferably, the number of repetitions of the cyclic prefix (CP) is equalto the number of repetitions of the basic sequences.

Preferably, the number of repetitions of the cyclic prefix (CP) isselected according to a detection performance of the generated sequence.

Preferably, the basic sequence is selected from a sequence set properlyselected according to the cell size in several sequence sets whichchange a zero-correlation-zone (ZCZ) length in proportion to the cellsize.

Preferably, the basic sequence is selected from a sequence set having afixed zero-correlation-zone (ZCZ) length irrespective of the cell size,and is selected from only some sequences having been selected accordingto a circular shift (CS) degree.

Preferably, the selected sequences can be distinguished from each otheraccording to a circular shift (CS) degree applied to the selectedsequences during when a Node-B performs sequence detection.

Preferably, the basic sequence is selected from a sequence set properlyselected according to the cell size in several sequence sets whichchange a cyclic prefix (CP) length in proportion to the cell size.

It is to be understood that both the foregoing general description andthe following detailed description of the present invention areexemplary and explanatory and are intended to provide furtherexplanation of the invention as claimed.

The present invention defines a detailed method for repeating thesequence according to the cell size or the increasing distance betweenthe UE and the Node-B, so that the Node-B receiving the RACH signal caneasily decide a timing point. Also, the present invention defines how toset the lengths of CP and ZCZ according to the cell size, so that it canmaintain orthogonality and solve the difficulty in distinguishingsequences.

If the ZCZ length is changed to another length according to the cellsize, the present invention can use many more sequences. If the CPlength and the ZCZ length are properly combined with each other, thepresent invention can reduce the number of signaling times of theNode-B.

BRIEF DESCRIPTION OF DRAWINGS

The accompanying drawings, which are included to provide a furtherunderstanding of the invention, illustrate embodiments of the inventionand together with the description serve to explain the principle of theinvention.

In the drawings:

FIGS. 1 and 2 are conceptual diagrams illustrating a variety ofprocesses encountered when the user equipment (UE) establishes an uplinkcommunication with the Node-B;

FIG. 3 is a configuration diagram illustrating a RACH signal structureused for a synchronization access and a non-synchronization access;

FIG. 4 is a conceptual diagram illustrating different requirementsaccording to UE's location within a cell;

FIG. 5 is a configuration diagram illustrating a basic RACH structureaccording to an embodiment of the present invention;

FIG. 6 is a configuration diagram illustrating an exemplary structure inwhich only a preamble is repeated when the RACH length is double thebasic length according to an embodiment of the present invention;

FIG. 7 is a configuration diagram illustrating an exemplary structure inwhich a preamble and a CP are repeated when the RACH length is doublethe basic length according to an embodiment of the present invention;

FIG. 8 is a conceptual diagram illustrating the number of iterations ofthe preamble and the CP when the RACH length is equal to a lengthcorresponding to predetermined number of times the basic lengthaccording to an embodiment of the present invention;

FIG. 9 is a conceptual diagram illustrating the relationship between around-trip delay (RTD) and the circular shift (CS) length applied to thesequence according to an embodiment of the present invention;

FIG. 10 is a conceptual diagram illustrating a method for maintaining adetection performance by selecting the ZCZ sequence on the conditionthat the cell is larger than a cell acquired when the ZCZ sequence isdesigned according to the present invention;

FIG. 11 shows a plurality of sequence sets for changing the CP lengthaccording to the cell size according to the present invention;

FIG. 12 shows a plurality of sequence sets for changing the ZCZ lengthaccording to the cell size according to the present invention;

FIG. 13 shows a plurality of sequence sets for changing the CP lengthaccording to the cell size and other sequence sets for changing the ZCZlength according to the present invention; and

FIG. 14 shows a plurality of sequence sets for simultaneouslyestablishing the CP length and the ZCZ length according to the cell sizeaccording to the present invention.

DETAILED DESCRIPTION OF THE INVENTION

Reference will now be made in detail to the preferred embodiments of thepresent invention, examples of which are illustrated in the accompanyingdrawings. Wherever possible, the same reference numbers will be usedthroughout the drawings to refer to the same or like parts.

Prior to describing the present invention, it should be noted that mostterms disclosed in the present invention correspond to general termswell known in the art, but some terms have been selected by theapplicant as necessary and will hereinafter be disclosed in thefollowing description of the present invention. Therefore, it ispreferable that the terms defined by the applicant be understood on thebasis of their meanings in the present invention.

Although the present invention will intensively disclose a method forextending a sequence in the form of an iterative sequence according tothe larger cell size and at the same time increasing the CP lengthand/or the ZCZ length according to the larger cell size, it will beobvious to those skilled in the art that the scope of the presentinvention is not limited to the above-mentioned method, and can also beapplied to another method associated with the longer distance betweenthe user equipment (UE) and the Node-B.

For the convenience of description and better understanding of thepresent invention, general structures and devices well known in the artwill be omitted or be denoted by a block diagram. Wherever possible, thesame reference numbers will be used throughout the drawings to refer tothe same or like parts.

FIG. 5 is a configuration diagram illustrating a basic RACH structureaccording to an embodiment of the present invention.

Referring to FIG. 5, “CP” is indicative of a cyclic prefix, and“Preamble” is indicative of a specific part in which a sequence (e.g.,CAZAC sequence) to be used for accessing the RACH channel is insertedafter having been generated in a time or frequency space. The remainingpart other than the CP and preamble parts in a total length of the RACHis a guard time.

The method for extending the sequence in the form of an iterativesequence is generically named a method for repeating (or iterating) thepreamble part.

If the sequence is repeated, not only unique characteristics (i.e.,length or correlation characteristics) of the sequence but also thevariation in cell size should be considered. If the cell size is changedto another size, the round trip delay (RTD) value and the delay spreadare also changed to others, so that they have a negative influence uponthe sequence design.

Next, a variety of methods available when the RACH length is doubledwill hereinafter be described in detail.

However, it should be noted that the above-mentioned example in whichthe RACH length is doubled will be disclosed for only illustrativepurposes, and can also be applied to other examples in which the RACHlength corresponds to predetermined times of a basic length.

FIG. 6 is a configuration diagram illustrating an exemplary structure inwhich only a preamble is repeated when the RACH length is double thebasic length according to an embodiment of the present invention.

Referring to FIG. 6, the CP and preamble lengths of FIG. 6 are equal tothe RACH basic structure, but it should be noted that only the preamblepart is repeated to generate the RACH signal, differently from the RACHbasic structure. This method allows the user equipment (UE) to simplyand repeatedly transmit the once-generated preamble without performingadditional operations, so that no additional complexity occurs in theUE. Also, the Node-B indicates only the RACH length without performingany other operations, so that the amount of signaling information isreduced.

If the RACH is repeated, each of the CP interval and the guard timeinterval is doubled, so that a spare or redundant space other than theCP and guard time lengths to be actually used remains.

The redundant space may be used as an additional guard time. Otherwise,if the RACH length is increased N times, and the redundant space hasenough length to include the preamble, the preamble is additionallyrepeated and transmitted, so that a detection performance may beimproved. The guard time has enough length to be adjusted, so that itcan be properly adjusted. In other words, an additional preamble may beinserted in the RACH by adjusting the length of the guard time.

As shown in FIG. 6, if only the preamble part is repeated and the CPpart is not repeated while the interference is created, the Node-B mayhave difficulty in detecting a starting point of the RACH signal. Forexample, if the Node-B detects the RACH signal of FIG. 6 using anauto-correlation method and acquires a desired timing point, theauto-correlation interval is equal to the preamble length, so that theNode-B may incorrectly detect the auto-correlation value by a specificvalue equal to a location corresponding to the CP length.

According to the above-mentioned timing detection method based on theauto-correlation, if the RACH signal experiences the delay spreadingduring the transmission process, the detection performance may begradually deteriorated in proportion to the degree of the delayspreading. In addition, although the Node-B detects the sequence in afrequency area to prevent the delay spreading from being generated, theinaccuracy or ambiguity corresponding to the CP length may unavoidablyoccur.

FIG. 7 is a configuration diagram illustrating an exemplary structure inwhich a preamble and a CP are repeated when the RACH length is doublethe basic length according to an embodiment of the present invention.

Referring to FIG. 7, the embodiment of FIG. 7 shows an exemplary case inwhich the CP is also repeated while the iterative sequence is generated,differently from FIG. 6.

The embodiment of FIG. 6 previously stated above does not repeat the CPpart while the iterative sequence is generated, so that the Node-B mayhave difficulty in detecting the starting point of the RACH signaltransmitted from the user equipment (UE).

However, the embodiment of FIG. 7 has only one completely-repeated partin the sequence, so that the Node-B can easily recognize the timingpoint of the RACH signal.

For example, provided that the Node-B detects a timing point of the RACHsignal using an auto-correlation method, the length of an establishedauto-correlation zone is equal to the sum of the CP length and thepreamble length. Therefore, the Node-B can acquire a peak value at onlyone timing point during the auto-correlation operation, so that it cancorrectly recognize the timing of the RACH signal.

Compared with FIG. 6, FIG. 7 has a smaller redundant space in the RACHspace during the generation time of the iterative sequence. If the RACHlength becomes longer in proportion to the cell size, the Node-B mayhave difficulty in inserting an additional iterative sequence caused bythe redundant space. However, if the guard-time length is adjusted, itshould be noted that the preamble can be additionally repeated.

In the case of generating the iterative sequence as described above, itis preferable that unique characteristics of the sequence, the cellsize, and the UE's location within a cell are considered.

Generally, if the cell size becomes larger, it is preferable that theRACH length may also be increased in proportion to the longer cell size.

However, as previously stated in FIG. 4, the RACH requirements may bedifferent in the distances from the UE to the Node-B. In more detail,although an objective UE is located in the cell, the RACH requirement isdifferently determined according to specific information indicatingwhere the corresponding UE is located in the cell (i.e., the distancefrom the UE to the Node-B).

The RACH requirements (i.e., the RACH length and/or the RACH width),which are different in the distances between the UE and the Node-B andan exemplary sequence structure applied to the RACH requirements, havebeen disclosed in Korean Patent Application Nos. 2006-87290 and2006-92836. According to the Korean Patent Application Nos. 2006-87290and 2006-92836, individual iterative parts of the iterative RACHstructure of FIG. 6 or 7 are used as timeslots, so that a specific UElocated at the center of the cell may access the RACH using only one ofthe timeslots.

According to the above-mentioned segmented access scheme, if only thepreamble is repeated without repetition of the CP, the RACH signal ofthe UE located at the center of the cell may collide with the RACHsignal of the other UE located at the boundary of the cell.

For example, provided that different CSs (Circular shifts) are appliedto the first UE located at the center part of the cell and the second UElocated at the boundary of the cell, and a sequence having orthogonalityis used, a variety of delays are applied to the iterative rear part ofthe RACH signal transmitted from the second UE, so that it is difficultto discriminate between the RACH signal transmitted from the second UEand the RACH signal transmitted from the first UE. This problem becomesmore serious when the RACH signal has a delay corresponding to adifference in quantity of the CS applied to both sequences.

Otherwise, if not only the preamble of FIG. 6 but also the CP is alsorepeated for the second UE located at the cell boundary, the Node-B caneasily detect the timing point of the RACH signal, so that thepossibility of generating ambiguity in the above-mentioneddiscrimination is reduced. And, if the rear part of the iterativesequence structure is located within a second slot of the RACHstructure, the possibility of correctly separating the orthogonalsequences from each other increases as described above.

Therefore, the sequence generation method according to the presentinvention increases the sequence length in proportion to the larger cellsize and the longer distance between the UE and the Node-B. In thiscase, not only the preamble part but also the CP part is also repeatedor iterated.

In the meantime, if the RACH length is increased N times, the number ofCPs to be inserted in the RACH may be set to “N”, however, it should benoted that the number of CPs can also be set to other numbers.

FIG. 8 is a conceptual diagram illustrating the number of iterationtimes of the preamble and the CP when the RACH length is equal to alength corresponding to predetermined times the basic length accordingto an embodiment of the present invention.

The example of FIG. 8 shows that the RACH length is equal to four timesthe basic structure, so that the CP is inserted in only two parts (i.e.,the first part and the center part). The reason why the CP is insertedin the center part is to allow the Node-B to easily detect the timingpoint.

The length of a correlation interval in a correlation calculationexecuted by the Node-B may be equal to the sum of the length of a singleCP and the length of two preambles. If the RACH length increases by Ntimes, and the length of the correlation interval is very long, the CPmay be more closely inserted in the RACH length. Needless to say, thenumber of inserted CPs cannot exceed the number of preamble iterations.

The following factors must be considered on the condition that thesequence is extended as described above, i.e., the round trip delay(RTD) and the sequence collision caused by the channel delay spread,detailed descriptions thereof will hereinafter be described.

FIG. 9 is a conceptual diagram illustrating the relationship between around-trip delay (RTD) and the circular shift (CS) length applied to thesequence according to an embodiment of the present invention.

For example, if the cell size is doubled, the round trip delay (RTD) isalso doubled, so that the ZCZ size must be more increased. In this way,if the CP length is longer than the RTD, orthogonality between a firstsequence of the Case 1 of FIG. 9 and a second sequence of the Case 2 ofFIG. 9 can be maintained.

The CS length used to construct the orthogonal sequence set in the CAZACsequence, i.e., the ZCZ length in the CAZAC sequence, must be longerthan the channel delay spread length, so that the ZCZ length must belonger than the CP length.

Therefore, in the case of using the circular shift (CS), it ispreferable that the CS length (i.e., the ZCZ length) in the CAZACsequence may be configured in units of an integer multiple of the sum ofthe RTD and the channel delay spread time. Also, the CS length may bedecided in consideration of the timing error, or may also be configuredin larger-sized units.

If the cell size is changed to another, it can be recognized that theRTD can easily exceed the CP interval, so that it is expected thatcorrelation characteristics are deteriorated. Therefore, it ispreferable that the CP length is also changed to another according tothe cell size.

The length of the available CS, i.e., the ZCZ length, may also bechanged to another according to the cell size. In other words, the ZCZlength is also changed according to the cell size, so that the size ofthe available orthogonal sequence set is also changed to another.

However, the sequence set having a predetermined ZCZ length may be usedas necessary. In the case of using the sequence set, a method forpreventing the detection performance from being deteriorated by the RTDand the delay spread should be considered.

Therefore, the following design standards are proposed.

FIG. 10 is a conceptual diagram illustrating a method for maintaining adetection performance by selecting the ZCZ sequence on the conditionthat the cell size is larger than a cell size acquired when the ZCZsequence is designed according to the present invention.

In FIG. 10, it is assumed that the ZCZ length is fixed according to thecell size considered when the initial sequence is designed. The definedZCZ sequence is set to “ZCZ(i,n)”, where “i” is an index of an originalsequence and “n” is a ZCZ index.

In this case, the ZCZ sequence is created when a sequence having apredetermined amount is circularly shifted in a time or frequency area.Also, the ZCZ is created when an exponential function is multiplied by asequence converted into another domain.

According to an embodiment of the present invention, if the sequencesets are pre-defined, the present invention provides a method fordifferently selecting a specific sequence to be actually used from amongthe defined sequence sets according to the cell size. In more detail,the present invention provides a method for employing only specificsequences each of which has a specific ZCZ sequence.

For example, under the condition that predetermined index values are setto n₁ and n₂, if one of the ZCZ(i,n₁) and the ZCZ(i,n₂) is transmittedfrom the center part of the cell (i.e., RTD=0), and the other one istransmitted from the boundary part of the cell (i.e., RTD=2*CellSize/Speed of Light), two sequences must not have the ambiguousdetection characteristics by the detection algorithm. If ambiguousdetection characteristics exist between the two sequences, one of thetwo sequences must not be used.

For the above-mentioned purposes, the Node-B must decide which one oforiginal indexes (i) will be used, and must perform a signaling processin which the Node-B informs the user equipment (UE) which one of ZCZindexes will be employed by the RACH, so that the Node-B requiresadditional information for the above-mentioned operations. Theaforementioned additional information may also be notified to userequipments over a channel such as a BCH.

According to the embodiment of FIG. 10, if the CS in the CAZAC sequenceis applied to a time area, a minimum unit of an initially-fixed ZCZ size(i.e., the available CS size) is fixed to a specific cell size, a methodfor applying the CS to a larger-sized cell is designed to use only thesequence having an odd-numbered index from among the ZCZ indexes. As aresult, the number of available ZCZ sequences is reduced, but theembodiment of FIG. 10 can correctly discriminate between signalssimultaneously while using the pre-defined sequence sets.

In the meantime, the above-mentioned method cannot reduce the ZCZ lengtheven when communication is established in a cell smaller than the cellsize considered when an initial sequence is designed, so that the numberof ZCZs is fixed even when the sequence is smaller than a specific cellsize.

FIG. 11 shows a plurality of sequence sets for changing the CP lengthaccording to the cell size according to the present invention.

In FIG. 11, the CP length is increased to cope with the RTD whichincreases by the larger cell size and the distance to the Node-B, butthe ZCZ length is fixed as shown in FIG. 10.

Needless to say, if the cell size or the distance to the Node-B isreduced in the embodiment of FIG. 11, the CP length may be reduced, andthe ZCZ length may not be changed to another.

If the ZCZ length is fixed, the ZCZ sequences, which may not bedistinguished from each other due to the larger cell size as shown inFIG. 10, must be excluded from the cell to be used. Also, the Node-Bmust inform the user equipment (UE) which one of ZCZ sequences can beused, and this information may also be notified to the user equipment(UE) over a channel such as a BCH.

If the cell size is small in the case of a second ZCZ sequence set (Set2) of FIG. 11, a third ZCZ sequence set (Set 3) indicates the set ofavailable sequences which can be used when the cell size is larger thanthe other cell size defined when the ZCZ interval is designed.

In the case of the third ZCZ sequence set (Set 3), it can be noted thatonly a sequence having a specific ZCZ index can be used as previouslystated in FIG. 10.

FIG. 11 shows a specific case in which only specific sequences, each ofwhich has an odd-numbered ZCZ index, are used. However, the CP length ofthe third ZCZ sequence set (Set 3) is longer than that of the second ZCZsequence set (Set 2), so that orthogonality between individual sequencesis not damaged.

In order to inform the user equipment (UE) of information of the CPlength, the Node-B may further include a predetermined process capableof transmitting the above-mentioned ZCZ index information and theCP-length information to the user equipment (UE) over the BCH. However,this method is unable to adjust the ZCZ length when the cell size of asystem is smaller than the initially-designed cell size, so that itprefers to fix the number of ZCZs.

FIG. 12 shows a plurality of sequence sets for changing the ZCZ lengthaccording to the cell size according to the present invention.

The embodiment of FIG. 12 does not consider the CP length, and removesthe ambiguity or difficulty in discriminating between sequences capableof accessing the RACH. FIG. 12 shows only the preamble part of the basicsequence other than the CP part.

As can be seen from FIG. 12, the ZCZ length of the third ZCZ sequenceset (Set 3) applied to a small-sized cell is longer than that of thesecond ZCZ sequence set (Set 1) applied to a large-sized cell. In moredetail, FIG. 12 shows that the ZCZ size (3) used for the large-sizedcell is designed to be larger than the ZCZ size (2) used for thesmall-sized cell. In brief, the smaller the cell size, the smaller theZCZ size.

If the ZCZ length is fixed to a specific value in the embodiments ofFIGS. 10 and 11, only a ZCZ sequence suitable for a specific conditionbased on the fixed length is selected.

If the ZCZ length (i.e., the available CS length (also called “Ncs”)) ischanged to another length according to the embodiment of FIG. 12, thereare generated many more ZCZ sequences than ZCZ sequences acquired whensome parts of ZCZ sequences are selectively used. If the cell sizebecomes smaller, the above-mentioned embodiment can define more ZCZs inthe same original sequence.

In this case, the index of the original sequence and the ZCZ sizeinformation must be notified as signaling information to the userequipment (UE), and they can also be applied to the user equipment (UE)over a downlink channel such as a BCH.

FIG. 13 shows a plurality of sequence sets for changing the CP lengthaccording to the cell size and other sequence sets for changing the ZCZlength according to the present invention.

The embodiment of FIG. 13 indicates that both the CP length and the CSlength are changed to others according to the cell size. The mostflexible design method is to select an optimum sequence set by selectingthe proper CP length and the proper ZCZ size according to the cell size.The embodiment of FIG. 13 optimally adjusts the number of sequences, andmaintains the perfect periodic correlation characteristics betweensequences.

Referring to FIG. 13, the user equipment (UE) can select an appropriatesequence set according to the size of a corresponding cell from amongsequence sets associated with the CP length. If the sequence set havinga specific CP length is selected, the embodiment of FIG. 13 can select asequence set, which has an appropriate ZCZ length according to the sizeof a cell including the UE, from among lower sequence sets classifiedaccording to the ZCZ length contained in the sequence set having theselected CP length.

Needless to say, in the case of selecting the sequence set having theproper CP length and the proper ZCZ length, the above-mentioned methodfor selecting the ZCZ length after selecting the CP length has beendisclosed for only illustrative purposes, and the order of selecting theCP length and the ZCZ length may be reversed as necessary.

In order to select the sequence set as described above, the Node-B mustindicate which one of the CP lengths will be used along with an originalsequence index to be used, and at the same time must indicate which oneof the ZCZ lengths will be used along with the same original sequenceindex, and this indication information may be transferred over adownlink channel such as a BCH.

In the meantime, the following scheme may also be used to reduce theamount of signaling information.

FIG. 14 shows a plurality of sequence sets for simultaneouslyestablishing the CP length and the ZCZ length according to the cell sizeaccording to the present invention.

The embodiment of FIG. 14 defines the sequence set capable ofsimultaneously changing the CP length and the ZCZ length according tothe cell size, and the Node-B selects a sequence set suitable for thesize of a corresponding cell from among sequence sets, and informs allthe cells of the selected sequence set.

For example, provided that the combination of the CP length and the ZCZlength is denoted by {CP1, ZCZ size 1}, {CP2, ZCZ size 2}, . . . , {CPN,ZCZ size N}, the Node-B selects the combination {CPi, ZCZ size i} as anappropriate combination suitable for its own cell size.

In this case, “CPi” and “ZCZ size i” between the combinations may beequal to each other, or may be different from each other.

Although FIG. 14 shows an exemplary combination in which the CP lengthand the ZCZ length are increased according to the larger cell size, itshould be noted that other combinations (e.g., a combination in whicheither one of the two lengths is not increased or reduced in some steps)may also be used as necessary.

If the CP length and the ZCZ length are selected as necessary in theembodiment of FIG. 14, the flexibility of the embodiment of FIG. 14 maybe lower than that of FIG. 13.

However, the Node-B need not inform each UE within the cell ofinformation associated with the CP length and information associatedwith the ZCZ length, and has to inform each UE of only index informationof the proper sequence set, so that the number of signaling objects isreduced.

If the ZCZ length is adjusted according to the above-mentionedembodiments, and the circular shift (CS) is not directly applied to thesequence and an exponential sequence is applied to the sequence, theinterval between frequency components is changed to another intervalaccording to the cell size.

In more detail, provided that two exponential sequences aree(k;f_(i),θ)=exp (−j2f_(i)k+θ) and e(k;f_(j),θ)=exp (−j2f_(j)k+θ), f_(i)and f_(j) are different from each other, and two RACH sequences are notdistinguished from each other in the detection algorithm, this meansthat the interval between the values f_(i) and f_(j) is very short, sothe interval should be increased more and more. As a result, it isunderstood that the CS length is changed to another length due to theabove-mentioned reason.

If the frequency interval is changed to another, a correspondingfrequency interval should be notified to the user equipment (UE) over adownlink channel such as a BCH. Also, the above-mentioned method foremploying the exponential function can be applied to only the CS on thecondition that there is no CP.

In this case, the CS length should be equal to the ZCZ size, should beconfigured in units, each of which is larger than the other unitcorresponding to the sum of the RTD and the channel delay spread, and aCS (Circular Shift) unit should be equal to an integer multiple of theabove-mentioned sum value or should be larger than the resultant integermultiple value.

The above-mentioned sequence definition method may define two sets toimplement the segmented access scheme, and may transmit the defined setsto a broadcast channel such as a BCH. In this case, the sequence set tobe used in the cell may not be equal to the other sequence set to beused outside of the cell, so that a broadcast method considering thissituation may also be used as necessary.

It should be noted that most terminology disclosed in the presentinvention is defined in consideration of functions of the presentinvention, and can be differently determined according to intention ofthose skilled in the art or usual practices. Therefore, it is preferablethat the above-mentioned terminology be understood on the basis of allcontents disclosed in the present invention.

It will be apparent to those skilled in the art that variousmodifications and variations can be made in the present inventionwithout departing from the spirit or scope of the invention. Thus, it isintended that the present invention cover the modifications andvariations of this invention provided they come within the scope of theappended claims and their equivalents.

As apparent from the above description, the present invention defines adetailed method for repeating the sequence according to the cell size orthe increasing distance between the UE and the Node-B, so that theNode-B receiving the RACH signal can easily decide a timing point. Also,the present invention defines how to set the lengths of CP and ZCZaccording to the cell size, so that it can maintain orthogonality andsolve the difficulty in distinguishing sequences.

If the ZCZ length is changed to another length according to the cellsize, the present invention can use many more sequences. If the CPlength and the ZCZ length are properly combined with each other, thepresent invention can reduce the number of signaling times of theNode-B.

The above-mentioned sequence generation method, the random accessmethod, and the signaling method for implementing the same can beproperly used for the 3GPP LTE system which is being intensivelystandardized.

However, besides the 3GPP LTE system, the present invention can also beequally applied to other wireless communication systems, which encountera sequence limitation due to the RTD variation affected by the cell sizeor the distance to the Node-B during the random access of the userequipment (UE).

Although the preferred embodiments of the present invention have beendisclosed for illustrative purposes, those skilled in the art willappreciate that various modifications, additions and substitutions arepossible, without departing from the scope and spirit of the inventionas disclosed in the accompanying claims.

What is claimed is:
 1. A method for performing a random access procedureby a Node-B with a specific user equipment (UE) within a cell in which aplurality of UEs are located together, the method comprising:transmitting system information for at least one of a basic sequenceindex and a length of a zero correlation zone (ZCZ) to the specific UE;and receiving a preamble sequence from the specific UE over a randomaccess channel, wherein the preamble sequence is generated from ConstantAmplitude Zero Auto-Correlation (CAZAC) sequences distinguishable by atleast one of the basic sequence index and a length of a Cyclic Shift(CS) applied to the preamble sequence, wherein the length of the CSapplied to the preamble sequence is given by one among a plurality ofapplication lengths determined based on the length of the ZCZ, wherein anumber of the plurality of lengths are differently given based on a typeof the specific UE, and wherein the system information is the same forall of the UEs within the cell regardless of the types of the UEs. 2.The method of claim 1, wherein the types of the UEs are based on alocation of each UE within the cell.
 3. The method of claim 1, whereinthe length of the CS applied to the preamble sequence is given one amongall lengths corresponding to a multiple of the length of the ZCZ withina limit of a length of the preamble sequence, when the type of thespecific UE is a first type.
 4. The method of claim 1, wherein thelength of the CS applied to the preamble sequence is given one among apart of all lengths corresponding to a multiple of the length of the ZCZwithin a limit of a length of the preamble sequence, when the type ofthe specific UE is a second type.
 5. The method of claim 1, wherein thesystem information is transmitted over a broadcast channel (BCH).
 6. ANode-B for performing a random access procedure with a specific userequipment (UE) within a cell in which a plurality of UEs are locatedtogether, the Node-B comprising: a transmitter configured to transmitsystem information for at least one of a basic sequence index and alength of a zero correlation zone (ZCZ) to the UE; and a receiverconfigured to receive a preamble sequence from the UE over a randomaccess channel, wherein the preamble sequence is generated from ConstantAmplitude Zero Auto-Correlation (CAZAC) sequences distinguishable by atleast one of the basic sequence index and a length of a Cyclic Shift(CS) applied to the preamble sequence, wherein the length of the CSapplied to the preamble sequence is given by one among a plurality ofapplicable lengths determined based on the length of the ZCZ, wherein anumber of the plurality of applicable lengths are differently givenbased on a type of the specific UE, and wherein the system informationis the same for all of the UEs within the cell regardless of the typesof the UEs.
 7. The Node-B of claim 6, wherein the types of the UEs arebased on a location of each UE within the cell.
 8. The Node-B of claim6, wherein the length of the CS applied to the preamble sequence isgiven one among all lengths corresponding to a multiple of the length ofthe ZCZ within a limit of a length of the preamble sequence, when thetype of the specific UE is a first type.
 9. The Node-B of claim 6,wherein the length of the CS applied to the preamble sequence is givenone among a part of all lengths corresponding to a multiple of thelength of the ZCZ within a limit of a length of the preamble sequence,when the type of the specific UE is a second type.